An acidic environment changes cyclin D1 localization and alters colony forming ability in gliomas

The influence of arsenic trioxide on the cell cycle, apoptosis and expression of cyclin D1 in the Jurkat cell line

Cyclin D1 drives cell cycle progression at the G1/S transition and is believed to play a significant role in tumorigenesis, contributing to efficient proliferation of many cancer cells. Consequently, it is also recognized as an end-point biomarker of therapeutic outcome for different treatment modalities in cancer. In this study we aimed to evaluate the expression and localization of cyclin D1 in arsenic trioxide (ATO) treated Jurkat cells (lymphoblastic leukemia cell line) and to correlate these results with the extent of cell death and/or cell cycle alterations. Jurkat cells were incubated with increasing concentrations of ATO (0.2, 0.6 and 1.0μM) for 24h in standard cell culture conditions. To reach our goal we performed annexin V/PI labeling for detection of cell death and RNase/PI labeling for evaluation of cell cycle distribution, which were followed by the respective flow cytometric analyses of ATO-treated Jurkat cells. Transmission electron microscopy was applied for visualization of the cell ultrastructure. For cyclin D1 estimation a biparametric cyclinD1/cell cycle assay was done and localization of the protein was shown after immuno-labeling using light microscopy (ABC procedure) and confocal fluorescence microscopy. We found that there were no significant changes in the percentages of cyclin D1-positive cells after the treatment with ATO, but at the same time mean fluorescence intensity reflecting cyclin D1 content was gradually increasing along with the cell cycle progression, irrespective of the applied dose of the drug. On the other hand, we found a nuclear-cytoplasmic shift of this protein as a major treatment-related response, which was in good accord with an increased rate of cell death and suggested that cyclin D1 cytoplasmic degradation is an important determinant of the therapeutic efficiency of ATO in the Jurkat cell line.

Involvement of tumor acidification in brain cancer pathophysiology

Gliomas, primary brain cancers, are characterized by remarkable invasiveness and fast growth. While they share many qualities with other solid tumors, gliomas have developed special mechanisms to convert the cramped brain space and other limitations afforded by the privileged central nervous system into pathophysiological advantages. In this review we discuss gliomas and other primary brain cancers in the context of acid-base regulation and interstitial acidification; namely, how the altered proton (H⁺) content surrounding these brain tumors influences tumor development in both autocrine and paracrine manners. As proton movement is directly coupled to movement of other ions, pH serves as both a regulator of cell activity as well as an indirect readout of other cellular functions. In the case of brain tumors, these processes result in pathophysiology unique to the central nervous system. We will highlight what is known about pH-sensitive processes in brain tumors in addition to gleaning insight from other solid tumors.

5-Benzylglycinyl-amiloride kills proliferating and nonproliferating malignant glioma cells through caspase-independent necroptosis mediated by apoptosis-inducing factor

5'-Βenzylglycinyl-amiloride (UCD38B) and glycinyl-amiloride (UCD74A) are cell-permeant and cell-impermeant derivatives of amiloride, respectively, and used here to identify the cellular mechanisms of action underlying their antiglioma effects. UCD38B comparably kills proliferating and nonproliferating gliomas cells when cell cycle progression is arrested either by cyclin D1 siRNA or by acidification. Cell impermeant UCD74A inhibits plasmalemmal urokinase plasminogen activator (uPA) and the type 1 sodium-proton exchanger with potencies analogous to UCD38B, but is cytostatic. In contrast, UCD38B targets intracellular uPA causing mistrafficking of uPA into perinuclear mitochondria, reducing the mitochondrial membrane potential, and followed by the release of apoptotic inducible factor (AIF). AIF nuclear translocation is followed by a caspase-independent necroptotic cell death. Reduction in AIF expression by siRNA reduces the antiglioma cytotoxic effects of UCD38B, while not activating the caspase pathway. Ultrastructural changes shortly following treatment with UCD38B demonstrate dilation of endoplasmic reticulum (ER) and mitochondrial swelling followed by nuclear condensation within hours consistent with a necroptotic cell death differing from apoptosis and from autophagy. These drug mechanism of action studies demonstrate that UCD38B induces a cell cycle-independent, caspase-independent necroptotic glioma cell death that is mediated by AIF and independent of poly (ADP-ribose) polymerase and H2AX activation.

The ubiquitin-proteasome system in glioma cell cycle control

A major determinant of cell fate is regulation of cell cycle. Tight regulation of this process is lost during the course of development and progression of various tumors. The ubiquitin-proteasome system (UPS) constitutes a universal protein degradation pathway, essential for the consistent recycling of a plethora of proteins with distinct structural and functional roles within the cell, including cell cycle regulation. High grade tumors, such as glioblastomas have an inherent potential of escaping cell cycle control mechanisms and are often refractory to conventional treatment. Here, we review the association of UPS with several UPS-targeted proteins and pathways involved in regulation of the cell cycle in malignant gliomas, and discuss the potential role of UPS inhibitors in reinstitution of cell cycle control.

CGGBP1 regulates cell cycle in cancer cells

Background

CGGBP1 is a CGG-triplet repeat binding protein, which affects transcription from CGG-triplet-rich promoters such as the FMR1 gene and the ribosomal RNA gene clusters. Earlier, we reported some previously unknown functions of CGGBP1 in gene expression during heat shock stress response. Recently we had found CGGBP1 to be a cell cycle regulatory midbody protein required for normal cytokinetic abscission in normal human fibroblasts, which have all the cell cycle regulatory mechanisms intact.

Results

In this study we explored the role of CGGBP1 in the cell cycle in various cancer cell lines. CGGBP1 depletion by RNA interference in tumor-derived cells caused an increase in the cell population at G0/G1 phase and reduced the number of cells in the S phase. CGGBP1 depletion also increased the expression of cell cycle regulatory genes CDKN1A and GAS1, associated with reductions in histone H3 lysine 9 trimethylation in their promoters. By combining RNA interference and genetic mutations, we found that the role of CGGBP1 in cell cycle involves multiple mechanisms, as single deficiencies of CDKN1A, GAS1 as well as TP53, INK4A or ARF failed to rescue the G0/G1 arrest caused by CGGBP1 depletion.

Conclusions

Our results show that CGGBP1 expression is important for cell cycle progression through multiple parallel mechanisms including the regulation of CDKN1A and GAS1 levels.

Dual inhibition of sodium-mediated proton and calcium efflux triggers non-apoptotic cell death in malignant gliomas

Malignant glioma cells maintain an elevated intracellular pH (pH(i)) within hypoxic-ischemic tumor microenvironments through persistent activation of sodium-proton transport (McLean et al., 2000). Amiloride has been reported to selectively kill human malignant glioma cell lines but not primary astrocytes (Hegde et al., 2004). While amiloride reduces pH(i) of malignant gliomas by inhibiting isoform 1 of sodium-proton exchange (NHE1), direct acidification was shown to be cytostatic rather than cytotoxic. At cytotoxic concentrations, amiloride has multiple drug targets including inhibition of NHE1 and sodium-calcium exchange. Amiloride's glioma cytotoxicity can be explained, at least in part, by dual inhibition of NHE1 and of Na(+)-dependent calcium efflux by isoform 1.1 of the sodium-calcium exchanger (NCX1.1), which increases [Ca(2+)](i) and initiates glioma cell demise. As a result of persistent NHE1 activity, cytosolic free levels of sodium ([Na(+)](i)) in U87 and C6 glioma cells are elevated 3-fold, as compared with normal astrocytes. Basal cytosolic free calcium levels ([Ca(2+)](i)) also are increased 5-fold. 2', 4'-dichlorobenzamil (DCB) inhibits the sodium-dependent calcium transporter (NCX1.1) much more potently than NHE1. DCB was employed in a concentration-dependent fashion in glioma cells to selectively inhibit the forward mode of NCX1.1 at ≤1μM, while dually inhibiting both NHE1 and NCX1.1 at ≥20μM. DCB (1μM) was not cytotoxic to glioma cells, while DCB (20μM) further increased basal elevated levels of [Ca(2+)](i) in glioma cells that was followed by cell demise. Cariporide and SEA0400 are more selective inhibitors of NHE1 and NCX1.1 than amiloride or DCB, respectively. Individually, Cariporide and SEA0400 are not cytotoxic, but in combination induced glioma cell death. Like amiloride, the combination of Cariporide and SEA0400 produced glioma cell death in the absence of demonstrable caspase activation.